A (fluoroaryl)borane compound, amongst of all, tris(pentafluorophenyl)borane, is an useful compound as a co-catalyst for promoting the activity of a metallocene catalyst (polymeric catalyst) used in a cation complex polymerization reaction. The metallocene catalyst has been receiving considerable attentions as a polyolefin polymeric catalyst.
J. Organomet. Chem., 2, 245 (1964) discloses an example method of taking out crystals (powders) of tris(pentafluorophenyl)borane, wherein a pentane solution of tris(pentafluorophenyl)borane is evaporated to dryness in vacuo at 20.degree. C. However, the yield of tris(pentafluorophenyl)borane produced by the above method out of bromopentafluorobenzene used as a raw material is as low as 30%-50%. In addition, this publication fails to disclose a purity of tris(pentafluorophenyl)borane thus taken out.
Japanese Laid-open Patent Application No. 247978/1994 (Tokukaihei No. 6-247978) discloses a method of crystallizing tris(pentafluorophenyl)borane out of an octane solution of tris(pentafluorophenyl)borane and a method of sublimating a toluene solution of tris(pentafluorophenyl)borane after evaporating the toluene solution to dryness as other example methods of taking out crystals (powders) of tris(pentafluorophenyl)borane. However, the yield of tris(pentafluorophenyl)borane produced by these methods is also as low as 53%-71%.
To take out the crystals (powders) of tris(pentafluorophenyl)borane out of the solution thereof, the solution is usually subjected to the evaporation to dryness or a heating and concentrating manipulation over a long period in the form of a solution. Also, tris(pentafluorophenyl)borane is generally stored (preserved) or transported/transferred in the form of a solution.
However, when tris(pentafluorophenyl)borane is subjected to the evaporation to dryness or the heating and concentrating manipulation over a long period in the form of a solution, it partially decomposes to, for example, pentafluorobenzene. To be more specific, if a solution of tris(pentafluorophenyl)borane is merely heated and concentrated, the above decomposition reaction is triggered and a large amount of pentafluorobenzene resides with tris(pentafluorophenyl)borane as a decomposition product.
In other words, to obtain the crystals of tris(pentafluorophenyl)borane by the conventional methods, the solution must be subjected to the heating and concentrating manipulation over a long period, during which tris(pentafluorophenyl)borane eventually starts to decompose, thereby lowering the purity thereof. Thus, the conventional methods have a problem that highly-pure crystals (powders) of tris(pentafluorophenyl)borane can not be isolated at high yield.
Also, while a solution of tris(pentafluorophenyl)borane is stored (preserved) over a long period, tris(pentafluorophenyl)borane eventually starts to decompose through the above decomposition reaction. Thus, there has been a demand for a method which can store (preserve) tris(pentafluorophenyl)borane over a long period.